1. Field of the Invention
The present invention relates to an encasing film for a galvanic element, an electrochemical store, an electrochemical storage system, a flexible film for an encasing of a galvanic element, and a method for determining a state variable of an electrochemical store.
2. Description of the Related Art
With greater and greater demand for alternative drive concepts, the electric drive is increasingly becoming the focus of consideration. For this purpose, lithium-ion batteries are developing into the key technology for modern automobile drives. Lithium-ion cells exist in various structural forms or cell types. One particular specific embodiment is formed here by so-called pouch cells or coffee bag cells. As is already obvious from the name, pouch cells are not dimensionally stable; the cell winding thereof is welded into a flexible “film bag.”
The flexible housing used represents several system-related challenges, however. The sealing seam of the cells must thus be leak-tight over the entire service life of the battery. This is made more difficult because the cells “breathe” during the cycling, i.e., their thickness varies as a function of the state of charge. In addition, a changing pressure difference exists between the cell interior and surroundings as a result of air pressure variations and the respiration of the cell. Furthermore, aging processes, which are expressed in degassing, for example, may result in inflation of the pouch cell. The significant weight advantage, the possible stacking, which is spatially very efficient, and the large aspect ratio, whereby heat may be dissipated outward very well, are thus to be considered to be safety-critical because of the possible inflation of the cell in the event of gas development. The sealing seams of the cell may thus open nonspecifically in the event of malfunctions and overpressure resulting therefrom in the cell interior. In the worst case, combustible gases such as electrolyte or decomposition products may reach the outside, which may result in fires or explosions under certain circumstances. To monitor this safety-critical state, sensors for pouch cells are of great significance.